The present invention relates to lifting jacks, and more particularly to lifting jacks of the type designed for use with vehicles, especially those vehicles having a bumper affixed to and extending from the frame thereof.
The use of lifting jacks with vehicles of various types is well known, most vehicles traditionally being provided with a lifting jack as a standard accessory thereto to facilitate the performance of certain minor repairs requiring the raising of a portion of the vehicle, such as the removal and replacement of wheels and tires. Typically, such standard vehicle jacks include an upright jack shaft, a load lifting assembly supported on and operably associated with the shaft for vertical movement therealong, and a bumper engaging member attached or affixed to the load lifting assembly to provide mechanical interconnection between the vehicle and the load lifting assembly of the jack. Various mechanical arrangements are utilized in the load lifting assemblies of such jacks to provide a means of operably associating the load lifting assembly with the jack shaft. In the vast majority of conventional jacks, the load lifting assembly includes a ratchet mechanism shiftably engagable with teeth formed in and arranged vertically on the jack shaft for effecting movement of the load lifting assembly vertically along the shaft. Lucker U.S. Pat. No. 2,743,903 and Achterberg U.S. Pat. No. 3,110,475 are examples of this type of conventional jack. In other conventional jacks, the upright jack shaft includes a threaded screw rotatable about a vertical axis, the load lifting assembly in such jacks being correspondingly threaded internally to permit mounting thereof on the screw of the jack shaft and to facilitate vertical movement of the lifting assembly along the shaft upon rotation of the screw. Examples of such conventional jacks are disclosed in Kelleher U.S. Pat. No. 2,013,918 and Lucker U.S. Pat. No.
As will be understood by those skilled in the art, when a load is applied to the load lifting assembly of any of these conventional jacks, such as occurs when the bumper engaging member thereof is brought into lifting engagement with the bumper of a vehicle during a lifting operation, torque is exerted upon the load lifting assembly causing it to rotate or pivot with respect to the jack shaft about a horizontal axis, thereby concentrating the frictional forces between the load lifting assembly and the jack shaft at a relatively small number of points of frictional contact therebetween. Since the various components of conventional jacks of this type are normally constructed of relatively strong, thick metal stock, such jacks nevertheless operate generally satisfactorily when utilized to lift automobiles or other relatively lightweight vehicles, the primary effect of the torque and resulting concentration of frictional forces created during operation of such jacks being to increase the amount of physical exertion required of the jack operator.
As a result of this inherent disadvantage in conventional jacks, certain modifications in conventional jacks have heretofore been suggested to attempt to reduce the frictional forces created during operation thereof. The use of a roller mounted in the load lifting assembly at one of the points at which the lifting assembly frictionally contacts the jack shaft during loading is proposed in each of the above-mentioned Lucker patents. However, the existence and effect of torque on the load lifting assembly during loading thereof are in no way alleviated in such jacks. In fact, the creation of torque in the load lifting assemblies of these jacks during loading thereof is actually designed into such jacks in order to insure the occurrence of contact between the roller and the jack shaft during the lifting operation. Thus, instead of alleviating the creation of torque in the load lifting assembly of such jacks, such provisions merely effect a substitution of rotational frictional contact between the roller and the jack shaft during loading for the sliding frictional contact which would occur between the load lifting assembly and the jack shaft if no such roller were utilized. At best, such provisions merely somewhat reduce the amount of friction created by the torque which results during loading.
It is the existence and effect of torque in the operation of conventional jacks of all types that renders them generally unsatisfactory, if not inoperable, for use with vehicles such as vans, heavy duty utility vehicles such as "pick-up" trucks and the like, and recreational vehicles and the like, which are generally substantially heavier than automobiles. The heavier load which such vehicles place upon the load lifting assembly of such jacks exerts a greater amount of torque on such assembly thereby also creating greater frictional forces. In certain instances, such jacks are wholly inoperative for lifting such vehicles and attempts to so use such jacks result only in the deformation or disfigurement of the vehicle bumper. While such conventional jacks may be operable in other instances to lift certain of such vehicles, a relatively great degree of physical exertion is required of the operator to overcome the frictional forces created and, in most instances, deformation or disfigurement of the bumper nevertheless results. For this reason, vans, recreational vehicles and other such heavier vehicles are not generally provided with an accessory bumper jack but are instead normally provided with a jack designed for lifting engagement of the vehicle axle which must be positioned and operated from below the axle of the vehicle.
In contrast to the above, the present invention provides a lifting jack specifically designed to isolate the effect of torque created during loading and to direct such torque to the jack shaft in a manner substantially preventing rotational movement of the load lifting assembly of the jack with respect to the shaft and reducing the friction therebetween. The present invention also provides a lifting jack which may be used with vans, recreational vehicles and the like in a manner substantially similar to conventional bumper jacks without distorting or disfiguring the bumpers of such vehicles.